1. Field of the Invention
The present invention relates to an ink jet recording apparatus that is applied, for example, for a printer or a facsimile machine, and to an ink jet head used for the ink jet recording apparatus, a nozzle plate used for the ink jet head, an apparatus for manufacturing the nozzle plate and a method for manufacturing the nozzle plate.
2. Related Background Art
An ink jet recording apparatus is known that records characters and images on a recording medium by employing an ink jet head wherein a plurality of ink chambers, made of a piezoelectric material for which a poling process has been performed, are arranged in parallel, and electrodes are mounted on two inner walls of the individual ink chambers, and wherein the piezoelectric material is deflected by selectively transmitting a drive pulse signal to these electrodes, and to thus discharge ink from a plurality of nozzle openings that communicate with the ink chambers.
This ink jet recording apparatus moves a carriage, on which the ink jet head is mounted, in the main scanning direction relative to the recording medium, and discharges ink from the nozzles of the ink jet head to print a dot pattern in a predetermined area. When one main scanning has been completed, the ink jet recording apparatus moves the recording medium a predetermined distance in the sub-scanning direction, and repeats the above described operation to print all the desired area. As ink jet recording apparatuses of this type, high image quality, low cost color printers have been produced for home use and for office use, and the number of units produced has been increasing, year by year.
In order to provide increased image quality for such an ink jet recording apparatus, an effective means is to reduce the discharge side diameters of nozzle openings that are formed in the nozzle plate of the ink jet head, and for the arrangement density of the nozzle openings to be increased. This is because the size of ink droplets can be decreased and the number of droplets that can be ejected at one time is multiplied. On the other hand, the diameters of the ink nozzle openings on the ink chamber side are large so that ink easily flows in. In other words, the inside of each nozzle opening formed in the nozzle plate is shaped so it tapers down to a circle having a small diameter on the discharge side (the ink outlet side) from a circle having a large diameter on the ink chamber side (the ink inlet side).
Since each of the nozzle openings is tapered, a further effect provided is that the speed at which ink is discharged is increased. And as the angle at which the nozzle openings are tapered becomes greater, an additional, corresponding increase in the ink discharge speed is obtained. However, when the angle of the taper becomes too great, a resulting problem is that ink discharged from a nozzle will either fly transversely or air will be sucked into the nozzle following the discharge of ink. Therefore, in order to ensure printing stability, the accurate formation of the tapered portion is important. And to provide high image quality, several hundreds of the above described nozzle openings must be stably, accurately formed at pitches of 70 to 300 μm.
Therefore, etching, injection molding, or a method that uses a laser beam is employed to accurately form nozzle openings. Above all, a method that employs an excimer laser beam to bore polymer, can quickly and appropriately, with an accuracy on the micro order, form holes or grooves at normal temperature, while under normal pressure, without thermal distortion or flash. Especially, since a laser beam that is passed through a mask is condensed by a lens and used for boring, tapered holes can be formed as described in Japanese Patent Laid-Open Application No. 2002-160371.
However, according to the technique described in Japanese Patent Laid-Open Application No. 2002-160371, wherein a laser beam is passed through a mask and is split into multiple beams that are thereafter condensed and passed through a single large lens to form a plurality of nozzle openings, as shown in FIG. 10, the laser beams passed, in this manner, through the portions of a lens 52 nearer the edges of the lens 52 are more affected by lens aberrations than are laser beams that are passed through the lens 52 near the center, and laser beam parallelism is deteriorated. Therefore, compared with nozzle openings 58P that have been bored by a laser beam passed through the lens 52 near the center, nozzle openings 58Q that have been bored by laser beams passed through the lens 52 nearer the edges will have shapes differing from that which is desired. Specifically, ink droplets discharged from the nozzle openings 58Q will not fly straight, and will land on a paper plane at an angle, degrading the printing quality. In order to avoid this problem, the laser beams must be passed through the lens 52 only near the center. Then, however, the number of nozzle openings 58 that can be formed at one time is reduced, and the processing efficiency is deteriorated when a large nozzle plate must be formed that has a total length equal to or greater than 20 mm.